Callandra Henderson Tyrol, better known by her nickname "Cally", is a young woman who works as a deckhand on Galactica.

During her tenure on Galactica, she falls in love with her boss, Galen Tyrol. Despite this, she and fellow deckhand Socinus, cover for Galen Tyrol on various occasions during Galen Tyrol's sexual interludes with Sharon "Boomer" Valerii, until Valerii is revealed as a humanoid Cylon. After this revelation, and a near death experience on Kobol, Henderson's anger and hatred for the Cylons leads her to "kill" Valerii during Valerii's transfer to a newly constructed brig.

Given 30 days in hack for unauthorized discharge of a firearm, she is lauded by her fellow crew members as a hero after her release. After reconciling with Galen Tyrol, their repaired relationship eventually amounts to a romantic one after Tyrol (suffering from suicidal dreams) savagely attacks Henderson after being awakened.

Henderson marries Tyrol, taking on his family name, and both muster out of the Colonial Fleet to settle on New Caprica in order to raise their son, Nicholas Tyrol. While on New Caprica, she is a part of the Colonial Workers Alliance, a labor union lead by Galen Tyrol. However, the Cylons' occupation of New Caprica destroys any dreams she had of a life on New Caprica: she is nearly executed as an "insurgent", but is later freed and returns to Galactica after the Second Exodus.

Life on Galactica, particularly with a child to take care of, causes strife within her marriage to Galen Tyrol. Additionally, she is the driving force into convincing Galen Tyrol to re-institute the Colonial Workers Alliance and press for an illegal strike. Unbeknownst to her, she is nearly executed by Marines at Admiral Adama's orders, under the charge that she is a mutineer. Later, despite an incident where she is nearly killed, the Tyrols try to save their marriage and put their family's interests first.

These efforts fail however, leaving her to take care of the child, which resorts on sleeplessness and dependence on anti-depressants and other medications. This strain is due to the revelation that Galen Tyrol is a Cylon, a fact Cally Tyrol discovers after following her husband to a weapons locker. After beating Galen Tyrol with a wrench, she attempts to kill Nicholas and herself by decompressing a launch tube; Tory Foster, another one of the Final Five, intervenes and manages to save Nicholas, but ejects Cally Tyrol into space. The crew on Galactica assumes that she committed suicide.

Henderson, as well as her boss, Galen Tyrol, seems prone to anger after a terrible event. Unlike Tyrol, Henderson tends to take decisive action as a result of her anger, rather than becoming immobile or overly irrational.

She is particularly adept at finding ways around the lack of replacement parts aboard Galactica. As Tyrol often comments, Henderson's small stature allows her better access to smaller spaces in the Vipers and Raptors she repairs.

Henderson survives the initial attacks to Galactica in the wake of the Fall of the Twelve Colonies, but loses many friends, including Prosna, a fellow deckhand, after the battlestar manages fire damage after being struck by a nuclear missile.

During an ill-fated mission to the Astral Queen, Henderson is nearly raped by prisoner Mason. He shoots her after she bites his ear off in defense. Henderson is returned to Galactica's sickbay for treatment, where she is given the nickname "Specialist Lazy" in jest by her comrades (Bastille Day).

Along with the rest of the deck crew, Henderson lies under oath to protect Chief Tyrol during a tribunal on a Cylon infiltration and attack (Litmus).

On a Raptor Scout team bound for Kobol (Kobol's Last Gleaming, Part I). Henderson's Raptor is attacked upon emerging from a Jump, resulting in a crash on Kobol. As one of the few that was relatively unhurt, Henderson later returns to the crash site with Chief Tyrol and Tarn, and barely makes it back alive with a forgotten medkit for Socinus (Scattered). However, the recovered medkit is too late to save Socinus, which greatly saddens Henderson (Valley of Darkness).

Crashdown gives Henderson an assuredly suicidal order as part of his attack to disable a Cylon anti-missile battery that threatens their expected SAR rescue. Henderson is so terrified that she freezes in place. Losing control, Crashdown threatens to shoot her if she does not obey. Just before Crashdown shoots Henderson, Dr. Gaius Baltar shoots him in the back, killing Crashdown instantly.

Seelix is shot in their retreat, but Henderson saves her life by carrying her further ahead. A rescue team of Raptors arrives, and Henderson returns to Galactica with the survivors (Fragged).

Henderson's anger transfers to Gaius Baltar when the Chief is arrested and accused of being a Cylon himself due to his past relationship with Boomer, and threatens to reveal Baltar's part in Crashdown's death if Baltar does not act to clear Tyrol's name.

Outraged by Tyrol's plight, Henderson shoots and kills Boomer (Resistance). Henderson is imprisoned in the brig but, at Tyrol's request, Commander Adama gives her a lenient sentence of 30 days for "discharging a firearm without permission" (The Farm).

Various crew members throw a party for Henderson's return to normal service.

Released from the brig, the deck crews give Henderson a welcome back party. Chief Tyrol is still upset with her for killing Boomer, although Henderson is grateful to the Chief for putting in a good word for her with Adama.

Henderson is disgusted when several drunken Pegasus crewmen brag about repeatedly raping the captured humanoid Cylon known as Gina, a reaction probably made stronger for her because Henderson herself survived an attempted rape.

Henderson pleads with Commander Adama to do something about the incident where Chief Tyrol and Helo are arrested by Pegasus command for the death of an officer that attempted to rape Caprica-Sharon (Pegasus).

After Commander Adama visits the hangar deck to confer with Laird on the status of the preparations for the planned attack, Adama takes Henderson aside and questions her about Laird. Henderson reveals Laird's origins that enforce Adama's increasing suspicions about Pegasus commander, Admiral Helena Cain.

Henderson wakes a sleeping Chief Tyrol up while he was in the midst of a suicidal nightmare. The delusional Tyrol gives Henderson a savage beating, quickly pummeling her into a bloody mess and knocking her unconscious. After a moment, Tyrol comes to his senses, shocked by what he had just done, and takes Henderson to sickbay, carrying her in his arms (Lay Down Your Burdens, Part I).

Henderson's jaw is wired shut to heal, but she forgives Tyrol and says she always cared about him. Interestingly, her feelings for Tyrol were apparently known to Cavil prior to his exposure as a humanoid Cylon (Lay Down Your Burdens, Part I).

Following suicide attacks by the insurgency led in part by her husband, Cally Tyrol is picked up by members of the New Caprica Police in a night-time raid. James "Jammer" Lyman, in his role with the NCP, discovers that she has been earmarked for execution, and asks Sharon Valerii to save her life. Valerii remarks that she does not know what she can do, as internal security is under the proviso of a different ministry. Henderson angrily tells Valerii to "go away and leave us alone" if she can't help her (Precipice).

Lyman later cuts her bonds and allows her to escape from the detention group slated for execution in a remote location. Chief Tyrol, arriving with a resistance sniper team, pushes his running wife out of the resistance's line of fire as they destroy the Cylon Centurion firing squad. She and her son hide in the resistance's underground bunker (Exodus, Part I).

After New Caprica

Cally Tyrol and her family are evacuated along with most of the human population of New Caprica. She is next seen resting on a bunk with her son in a room overcrowded with refugees. Her husband visits her after he and the Circle secretly execute James Lyman for having collaborated with the Cylons. Before his death, Lyman tells Galen that he saved his wife on the planet. When Galen inquires as to how she escaped the execution and if anyone helped her, she replies that "one of these goons" set her free. She asks her husband how he knows about that, apparently unaware of his role in the Circle (Collaborators). Later she is working alongside Chief Tyrol on the hangar deck again. It is unknown specifically who babysits their son Nicholas when both parents are working (Torn), but formal daycare arrangements seems to have been established for families with dependent children (A Day In The Life) that the Tyrols use.

Tyrol attends the ship-wide boxing match with her husband and son and watches from the sidelines as her husband fights and defeats Admiral Adama (Unfinished Business). She recovers from decompression sickness injuries sustained in an explosive decompression incident while being rescued from a depressurizing airlock along with her husband (A Day In The Life).

Death

Tyrol's relationship with her husband deteriorates as he becomes consumed with his discovery, unknown to her, that he is a Cylon. She grows angry at his constant absence, some of which is due to his meeting with fellow Cylons Foster, Tigh, and Anders. Moreover, she develops a sleeping disorder and becomes reliant on medication. Awakening one night to find him out of bed and out of their quarters, she finds him in Joe's bar with Foster and witnesses Foster making a pass at him. Tyrol confronts him in a rage, assuming that he is having an affair.

Later, she finds a note in their cabin with instructions for a time and place for a meeting. Thinking that it is a note from Foster, she goes to the place of the rendezvous, only to discover her husband, Tigh, and Foster going into a weapons locker together and closing the hatch. She opens a panel in the corridor and squeezes into a crawlspace where she can hear what her husband and the others are saying. To her horror, she discovers that her husband is a Cylon. She makes a noise, which the others hear. In her flight from the crawlspace, Tyrol leaves the wall panel ajar, which Foster discovers. When Galen returns to their cabin, she knocks him unconscious with a heavy wrench and then takes Nicky to the hangar deck, intending to commit murder-suicide by expelling him and herself out a Viper launch tube. Before she can do so, Foster shows up, convinces her to stop, and then offers to carry Nicky. As soon as Tyrol turns her son over, however, Foster knocks her down and takes Nicky into the control room, from which she expels Tyrol into space. The scene ends with a final shot of Tyrol's frozen, dead face drifting in space (The Ties That Bind). Her husband, for now, is unaware of Foster's role in Cally's death and believes Cally committed suicide because of her mistaken belief that he and Foster were having an affair. ("Escape Velocity")

During the Battle of the Colony Galen briefly links memories with the other Final Five members, this allows him - as well as the others - to see the truth of what Foster did and he flies into a rage and breaks her neck. Though this is problematic at a critical point (since it betrays a bargain made with Cavil to end the war) both Ellen and Tigh understand Tyrol's actions and Cally is avenged.

Notes

Cally's full name was not known during the first 2 seasons of the series (even though she is a character that has appeared since the opening minutes of the Miniseries), and during this entire time was known simply as "Cally". It was unknown then whether "Cally" was her given name or her surname; many assumed it was her surname and referred to her as "Specialist Cally" (in "The Farm", Chief Tyrol referred to her as "Specialist Cally"). However, actress Nicki Clyne, who plays Cally, has said she always thought of it as her character's given name. Her full name "Cally Henderson" was used in Season 3 to label props such as her locker, but isn't visible on screen. She took on Chief Galen Tyrol's surname after marrying him. After the character's death, Henderson's complete birth name, Callandra, is revealed at her funeral service in "Escape Velocity".

The Miniseries novelization (which is treated as a separate continuity source) gives her full name as "Jane Cally". However this was made up without the input of the BSG writing team, who later decided that Cally was actually her first name. The novel Sagittarius Is Bleeding, meanwhile, gives her name as Callista Henderson.

According to Ronald D. Moore's blog, Henderson's term of required service ended at the same time that Galactica was to be decommissioned. She was about to be honorably discharged and return to civilian life when the Cylons attacked, ending those plans.

In the DVD commentary for "Bastille Day", David Eick and Ron D. Moore elaborate on the increased role of Cally as the series progressed from the Miniseries through season 2:

Eick: Nicki Clyne, who you see here playing Cally, was somebody who in the Miniseries, I remember Michael (Rymer) and I cast just on the basis of her look, 'cause we thought she was really cute, she kind of reminded us of a young Shelley Duvall. [...] she turned out to be so good that we— in launching the series we started talking about ways to involve her and I'm very proud of a moment coming up where she does something rather nasty, that...

RDM: Well she almost died! She was gonna die in the intial drafts of this.

Eick: That's right! He kills her! He rapes and kills her! And they're telling us we're too dark this year.

RDM: Oh, I know. The second season is so much darker. And I don't think they even care. Yeah, Cally, Nicki, I hate to tell ya, but the bullseye was on Nicki here. And I can't even tell you why we decided it was, no I take that back I think it was your note; you said you wanted Cally to fight back and really show some balls in this scene. She bit his ear off...

Eick: I said, "She bites his frakking ear off" and I was totally being...you know, just illustrative! I didn't really mean it!

RDM: And I wrote, "she bites his ear off"!

Eick: "And I got the draft, and she bites his ear off! I was like "that's great!"

RDM: And from that moment on, I think, she really became part of the show. In a real sense, once she had gone through that and survived, and you know Tyrol and the gang come in and see her in the hospital at the end you kind of felt like she is one of the family.

Eick: Yeah, and she's taken on, in season 2 actually, a much, much, much more prominent role. You have no idea how prominent a role.

RDM: Which is really illustrative of the rise and fall of characters. I mean Boxey we thought going in was just going to be part of the show, and we just never really got our feet underneath us in terms of his storyline and really how it fit into it, and Cally who's just this 'other mechanic' at the beginning, who's just hanging around with Tyrol becomes a key element and part of the fabric of the show itself.

In the DVD commentary for "Bastille Day", RDM revealed how he came up with names for deckhands Cally, Socinus, and Prosna: "They were all names I pulled out of an 'ancient names internet site'. I literally, I found something on the internet that would give me like 'ancient names', I went through it and found those names. It was like ancient Greek and Roman...somethings. They might be, for all I know they're names for utensils, or something like that..."

↑This number comes from the serial number on the Dogtags Auctioned by the studios at the end of filming the series. These Screen used Tags also Read "S. Luman ser. 205873" Instead Nicki herself has mentioned the first few season dogtags were wrong.